cartesian_product.rs

fn cartesian_product(scale: &mut (u32, u32)) -> Vec<(u32, u32)> {
    (0..5)
        .flat_map(|a| (0..5).map(|b| (a * scale.0, b * scale.1)))
        .collect()
}

// error[E0373]: closure may outlive the current function, but it borrows `a`, which is owned by the current function
//  --> src/main.rs:7:34
//   |
// 7 |         .flat_map(|a| (0..5).map(|b| (a * scale.0, b * scale.1)))
//   |                                  ^^^  - `a` is borrowed here
//   |                                  |
//   |                                  may outlive borrowed value `a`
//   |
// note: closure is returned here
//  --> src/main.rs:7:23
//   |
// 7 |         .flat_map(|a| (0..5).map(|b| (a * scale.0, b * scale.1)))
//   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
// help: to force the closure to take ownership of `a` (and any other referenced variables), use the `move` keyword
//   |
// 7 |         .flat_map(|a| (0..5).map(move |b| (a * scale.0, b * scale.1)))
//   |                                  ^^^^^^^^